1. Field of the Invention
The invention in general relates to a multi-frame overdriving circuit of a liquid crystal display (LCD) and a method and an overdriving unit, and more particularly to a multi-frame overdriving circuit of an LCD and a method and an overdriving unit capable of reducing motion blur.
2. Description of the Related Art
The response time of a liquid crystal molecule has much to do with the cross-voltage at two ends of the liquid crystal molecule, and an overdriving method is normally used for increasing the response speed of the liquid crystal molecule. On the part of large-scale liquid crystal panel, a dual-frame overdriving method is further used for improving the response time of overall liquid crystal molecules to compensate corresponding image frames.
FIG. 1 shows a perspective of a conventional dual-frame overdriving circuit. The dual-frame overdriving circuit 100 includes a buffer 110, a first overdriving unit 120 and a second overdriving unit 130. The buffer 110 receives and stores the pixel data corresponding to a pixel. When the pixel data corresponding to the pixel changes to a second gray value from a first gray value in a first frame period, the first overdriving unit 120 outputs the first overdriving pixel data OD1 according to the first gray value and the second gray value in the first frame period. The second overdriving unit 130 outputs the second overdriving pixel data OD2 according to the first gray value and the second gray value in a second frame period next to the first frame period. However, when the pixel data changes to a higher gray value from a lower gray value, as liquid crystal molecules rotate slower at lower gray value, motion blur will occur on the image frame and thus the display quality of the image frame is deteriorated. The conventional dual-frame overdriving method can only compensate the image up to two frame periods.
When an image is moving at a fixed speed viewable to the naked eyes, a dynamic image with shorter width will result in shorter motion blur on the image frame, and a dynamic image with wider width will result in longer motion blur on the image frame. Referring to FIG. 2A, a perspective of motion blur on a conventional image frame is shown. In FIG. 2A, dynamic images A, B and C (dotted areas) with different data widths respectively result in motion blurs A′, B′ and C′ with different lengths. For example, the motion blurs A′, B′ and C′ respectively keep three, four and five frame periods. When the motion blurs A′, B′ and C′ keep more than two frame periods, the conventional dual-frame overdriving technology can not perform complete compensation, causing abrupt indention to the transmittance curve of liquid crystal molecules in the third frame period as indicated in FIG. 2B. Thus, the display quality of the image frame can not be improved.